非递归遍历二叉树之中序遍历

//中序遍历
int inorder_tree_walk(BinTreeNode * root){

    if(root == NULL){
        return -1;
    }
    stack<BinTreeNode *> s;
    BinTreeNode * p = root;
    while(!s.empty() || p != NULL)
    {
        while(p != NULL){
            s.push(p);
            p = p->lchild;
        }

        p = s.top();
        s.pop();
        cout << p->key<< endl;

        p = p->rchild;
    }
    return 0;
}

int insert(BinTreeNode * root, BinTreeNode * node){

    if(root == NULL || node == NULL)
    {
        cout << "insert root and node should not be NULL" << endl;
        return -1;
    }

    BinTreeNode * p = root;

    while(p != NULL){

        if(node->key < p->key){
            if(p->lchild == NULL){
                p->lchild = node;
                return 0;
            }
            else
                p = p->lchild;
        }
        else{
            if(p->rchild == NULL){
                p->rchild = node;
                return 0;
            }
            else
                p = p->rchild;
        }
    }

    return 0;
}

typedef struct BinTreeNode{
    int key;
    char * data;
    BinTreeNode * lchild;
    BinTreeNode * rchild;
}BinTreeNode;

typedef struct BinTree{
    int size;
    BinTreeNode * root;
}BinTree;

int main()
{
    BinTreeNode root;
    memset(&root, 0, sizeof(root));
    root.key = 9;

    BinTreeNode* btn;
    for(int i=0; i<10; i++)
    {
        btn = (BinTreeNode *) malloc(sizeof(BinTreeNode));

        memset(btn, 0, sizeof(btn));
        int k = i*13155443 % 17;
        cout << k << " ";
        btn->key = k;
        insert(&root, btn);
    }
    cout << endl;

    inorder_tree_walk2(&root);

    return 1;
}